1. Field of the Invention
This invention relates to a card such as a prepaid card. More particularly, it relates to a card having superior gate-access properties with respect to a read-write head and also being biodegradable.
2. Description of the Related Art
In recent years, identification (ID) cards or membership cards which identify yourselves and cash cards, credit cards, prepaid cards, commutation ticket cards, coupon ticket cards or the like which have cash values are being used in many fields.
Among these, the prepaid cards are comprised of a card in which some information of value corresponding to an amount of money prepaid in a certain unit is recorded. In such prepaid cards, a print layer formed of characters or letters, patterns or designs, bar codes or the like or a magnetic recodeing layer or optical recording layer is provided on a substrate, and the value information or distinguishing information for the prepaid cards is read from or written in that layer through a read-write head. Accordingly, the prepaid cards are required to satisfy gate-access properties (mechanical properties required when the card is applied to the gate of a read-write head, as exemplified by durability, folding endurance and rigidity) good enough for the cards to be applicable to such a read-write head and yet required to be manufactured with ease. Hence, as a supporting substrate serving as a structural material of the prepaid cards, polyethylene terephthalate (PET) resin is mainly used.
In the case of ID cards, membership cards, cash cards, credit cards and so forth, polyvinyl chloride (PVC) resin is also commonly used as the supporting substrate.
Now, these cards are put away when used up, and most of them are buried and given away in soil in waste disposal grounds. Since, however, the PET and PVC constituting the supporting substrates of these cards are not biodegradable, they are not degraded and turn into semi-permanent refuse with their shapes remaining as they are. Thus, there is an anxiety about bad influence on natural environment.
Hence, as supporting substrates for such cards, it has been attempted to use paper substrates made of paper, which is a biodegradable natural material. It has been also proposed to use biodegradable resin substrates (Japanese Patent Applications Laid-open No. 5-42786 and No. 5-85088) comprised of photodegradable or biodegradable synthetic resins (Japanese Patent Applications Laid-open No. 57-150393, No. 59-220192, No. 51-93991, No. 63-260912 and No. 57-150393). It is still also proposed to use a biodegradable resin coated paper substrate formed by lamination of a thin film of a biodegradable resin of the same kind as the above (Japanese Patent Application Laid-open No. 7-9788).
In the case of the paper substrates, however, there has been the problem that card properties such as durability, folding endurance, water resistance, chemical resistance, surface smoothness, glossiness and workability required for cards can not be well satisfied. Hence, the cards making use of paper as supporting substrates are used in cards of disposable types such as pass tickets, admission tickets and railroad tickets, which are thrown away after used once, but it has been difficult for such cards to be used in prepaid cards or the like which are repeatedly used reasonably many times for a certain period of time. In this case, for the purpose of improving the mechanical properties of the paper substrate, one may contemplate to laminate synthetic resin such as polyethylene, polypropylene, polyvinyl chloride or polyethylene terephthalate or a metal foil such as aluminum foil to its surface as a protective layer. Since, however, these materials for such a protective layer exhibit no sufficient biodegradability, the protective layer itself turns into semi-permanent refuse and also the paper substrate remaining on the inner side of the protective layer becomes biodegradable with difficulty. There has been such a problem.
In the case of the biodegradable resin substrates, there have been the problems that they are available in a high cost and also they are unsatisfactory in mechanical properties such as folding endurance and rigidity.
In the case of the biodegradable resin coated paper substrates, water may soak into cards from their edges when the cards are immersed in water, e.g., when the cards are washed by oversight, to cause the cards to curl or elongate or cause their edges to turn up, leaving a problem on its water resistance. Hence, the applicability of such cards to read-write heads may become very low.